<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <select>
        <!-- <option value=""></option> -->
    </select>
    <button>选择星期二</button>
    <script>
        // const arr = ['周一', '周二', '周三', '周四', '周五', '周六', '周日']
        // const select =document.querySelector( 'select');
        // const btn = document.querySelector( 'button')
        // const selectContent = arr.map( (item,index) => `<option value="${item}">${item}</option>`)
        // // const selectContent = arr.map( (item,index) => `<option value="${index + 1}">${item}</option>`)
        // select.innerHTML = `<option value="">--星期--</option>` + selectContent.join("");
        // btn.addEventListener( 'click', function(e) {
        //     // console.log(111)
        //     select.value = "周二";
        // })

        let arr = [1, 2, 3]
        console.log(arr.map((item, index) => {
            return `<li>item</li>`
        }))
        const brr = []
        console.log(arr.forEach((item, index) => {
            brr[index] = `<li>${item}</li>`
        }))
        console.log( brr)

        let obj = {'0':1,'1':2,'2':3}
        console.log( obj)
        console.log( arr)
        // obj['a']
        // obj.b

        // for(let i = 0;i < arr.length; ++i) {

        // }
        // for (const key in obj) {
        //     console.log( obj[key])
        // }
    </script>
</body>

</html>